Learn

Saturday, 31 October

JEE Main 2021 · PhysicsMultiple choiceDiagram basedMediumMulti-step

JEE Main 26 August 2021, Shift 2, Physics Q13

Question 13 of 90 in this shift, Physics question 13 of 30, Section A.

Two blocks of masses 3 kg and 5 kg are connected by a metal wire going over a smooth pulley. The breaking stress of the metal is 24π×102 Nm−2\frac{24}{\pi}\times10^{2}\ \mathrm{Nm^{-2}}. What is the minimum radius of the wire ? (take g=10 ms−2\mathrm{g}=10\ \mathrm{ms^{-2}})

The figure, in words

A pulley hangs from a ceiling; a wire goes over it with a block labelled 3 kg hanging from the left side and a block labelled 5 kg hanging from the right side (lower than the 3 kg block).
  1. (1)12.5 cmOfficial answer
  2. (2)125 cm
  3. (3)1250 cm
  4. (4)1.25 cm

Official answer

Option 1

NTA final key.

Chapter
Mechanical Properties of Solids
Topic
Elasticity
Idea tested
Breaking Stress and Breaking Force

Same idea in other shifts

Asked 7× in all
  1. 5 Apr 2026, Shift 1 · Q43Two wires as shown in the figure below, made of steel and have breaking stress of 12×108 N/m212 \times 10^8\ \mathrm{N/m^2}. Area of cross-section…MediumSingle correctHas a figure
  2. 6 Apr 2026, Shift 1 · Q30A lift of mass 1600 kg is supported by thick iron wire. If the maximum stress which the wire can withstand is 4×1084\times10^8 N/m2^2 and…MediumSingle correct
  3. 26 Jul 2022, Shift 2 · Q50The area of cross section of the rope used to lift a load by a crane is 2.5×10−4m22.5 \times 10^{-4}m^2. The maximum lifting capacity of the crane…EasySingle correct
  4. 29 Jul 2022, Shift 2 · Q53A metal wire of length 0.5 m and cross-sectional area 10−4 m210^{-4}\ \mathrm{m^2} has breaking stress 5×108 Nm−25\times10^8\ \mathrm{Nm^{-2}}. A block…MediumNumerical value
  5. 27 Aug 2021, Shift 2 · Q24Wires W1W_1 and W2W_2 are made of same material having the breaking stress of 1.25×109 N/m21.25\times10^9\ \mathrm{N/m^2}. W1W_1 and W2W_2 have…MediumNumerical valueHas a figure
  6. 9 Jan 2020, Shift 1 · Q23A body of mass m=10 kg is attached to one end of a wire of length 0.3 m. The maximum angular speed (in rad s−1\mathrm{s^{-1}}) with which…MediumNumerical value

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. This question needs a figure we do not reproduce; it is described in words above. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.